Resend frames when dynamic brightness changes on static CSS

The processing loop skipped resending when the CSS frame was
unchanged (static source). With a dynamic brightness value source
(e.g. audio), brightness can change every frame while colors stay
the same. Now compare effective brightness against previous value
and resend when it differs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/core/processing/wled_target_processor.py

@@ -486,6 +486,7 @@ class WledTargetProcessor(TargetProcessor):
         stream = self._css_stream
         prev_frame_ref = None
         has_any_frame = False
+        _prev_brightness = -1  # force first send
 
         # Pre-allocate brightness scratch (uint16 intermediate + uint8 output)
         _bright_u16: Optional[np.ndarray] = None
@@ -574,14 +575,16 @@ class WledTargetProcessor(TargetProcessor):
                             await asyncio.sleep(frame_time)
                             continue
 
-                        if frame is prev_frame_ref:
-                            # Same frame — keepalive or skip
+                        cur_brightness = _effective_brightness(device_info)
+
+                        if frame is prev_frame_ref and cur_brightness == _prev_brightness:
+                            # Same frame + same brightness — keepalive or skip
                             if self._needs_keepalive and has_any_frame and (loop_start - last_send_time) >= keepalive_interval:
                                 if not self._is_running or self._led_client is None:
                                     break
                                 send_colors = _cached_brightness(
                                     self._fit_to_device(prev_frame_ref, _total_leds),
-                                    _effective_brightness(device_info),
+                                    cur_brightness,
                                 )
                                 if self._led_client.supports_fast_send:
                                     self._led_client.send_pixels_fast(send_colors)
@@ -605,10 +608,11 @@ class WledTargetProcessor(TargetProcessor):
 
                         prev_frame_ref = frame
                         has_any_frame = True
+                        _prev_brightness = cur_brightness
 
                         # Fit to device LED count and apply brightness
                         device_colors = self._fit_to_device(frame, _total_leds)
-                        send_colors = _cached_brightness(device_colors, _effective_brightness(device_info))
+                        send_colors = _cached_brightness(device_colors, cur_brightness)
 
                         # Send to LED device
                         if not self._is_running or self._led_client is None: